Small-sized reduction gear with radial beam between axially extending columns of a carrier

ABSTRACT

A small-sized reduction gear includes: a stationary internal gear 10; a movable internal gear 20 having an internal gear; planet gears 12 in mesh with the stationary internal gear 10 and the movable internal gear 20; a holder member 15 and a holder clamp 19 which hold the planet gears 12; and a sun gear 4 in mesh with the planet gears 12 and directly connected with a motor shaft 3. The reduction gear further includes a column beam 18 provided between columns extending upwardly from the holder member 15 and, further guide sections provided in those sections where the movable internal gear 20 and the stationary internal gear 10 are in contact with each other. This construction helps to provide a small-sized reduction gear which makes it possible to obtain a high reduction ratio with a very small number of parts, which has a high level of transmission efficiency, which involves little backlash and noise, and which excels in dustproofness and can be produced at low costs. Further, it can be incorporated, together with a motor, into a cylinder to be rotated, so that a substantial reduction in size can be attained as compared to the case where the gear is outside the cylinder, thus realizing a space saving structure. Further, in this structure, the volume of the sound outwardly emitted can be reduced to a very low Level, thereby attaining a reduction in noise.

TECHNICAL FIELD

Recently, various products are required to be reduced in size,increasing the demand for miniaturization of driving devices, such as amotor, mechanism elements, such as a reduction gear. The presentinvention, which aims to meet such demand, relates to speed reductionmechanism of a small-sized reduction gear which is directly connected toa driving device such as a small-sized motor.

BACKGROUND ART

FIG. 5 shows an example of a conventional small-sized reduction gear ofthis type, which employs a planetary gear mechanism. In FIG. 5, a sungear 103 is fitted onto a shaft 102 which is at the center of asmall-sized motor 101. A lower case 104 is threadedly connected with thesmall-sized motor 101, with the motor shaft 102 serving as a commoncentral axis. The lower case 104 is equipped with an internal gear 105,and two to four planet gears 106 are provided between the internal gear105 and the sun gear 103. The plurality of planetary gears 106 mesh withthe sun gear 103, and mesh with the internal gear 105. The centers ofthe plurality of planet gears 106 are connected by a holder member 107,and an output shaft gear 109 is provided at the center of the holdermember 107. An intermediate carrier member 108 is connected to the lowercase 104 and constitutes a bearing for the output shaft gear 109. Theoutput shaft gear 109 is in mesh with the planet gears 106 which are inmesh with the internal gear 105. The gear at the center provides adriving force, which is transmitted through the planet gears 106 to theholder member 107 so as to rotate the same. The components which arethus operatively connected constitute a unit. When a high reductionratio is to be obtained, a number of such units are stacked one uponanother. In the last stage of this stacked structure, an output shaft110 exists at the center of rotation of the holder member 107.

Further, Japanese Patent Laid-Open No. 1-316545 1-316546, filed by thepresent inventors, disclose small-sized reduction gears using aplanetary gear mechanism. These reduction gears provide an improvementover the above-described conventional reduction gear.

In small-sized reduction gears using a planetary gear mechanism havingsuch a conventional construction, speed reduction is effected in thecourse of transmission from the sun gear 103 to the holder member 107through the planet gears 106. In such reduction gears, the reductionratio effected by one planetary gear unit is small, so that a largenumber of units must be stacked together before a large reduction ratiocan be obtained. Since a large number of gears are thus combined toeffect speed reduction, a great number of gear parts have to be used,resulting in high production costs. Further, this involves a high noiselevel, as well as a poor transmission efficiency and much backlash dueto the mesh of a large number of gears. The small-sized reduction gearsaccording to Japanese Patent Laid-Open No. 1-316545 and 1-316546 haveother problems. For example, they have a low rupture strength againstexternal forces, and are liable to be disabled from functioning properlywhen deformed by external forces.

The present invention aims to solve these problems in the prior art. Itis an object of the present invention to attain a reduction in thenumber of parts and production costs and to provide, at low costs, ahighly strong small-sized reduction gear which is small and light inweight, which involves low noise, which provides a high reduction ratioand a high level of transmission efficiency, and which offers highrupture strength despite its small size.

DISCLOSURE OF THE INVENTION

In accordance with the present invention, there is provided asmall-sized reduction gear having a stationary internal gear 10 havingan internal gear whose number of teeth is n; a movable internal gear 20having an internal gear whose number of teeth is n± m, where m equals 1through 4 two planet gears 12 gears each having Z external teeth whichare in mesh with the stationary internal gear 10 the movable internalgear 20; a holder member 15 and a holder clamp 19 which hold the planetgears 12; and a sun gear 4 which has e teeth in mesh with the planetgears 12 and which is directly connected with a motor shaft 3;

wherein

(1) a support beam 18 is provided between columns 15c extending upwardlyfrom the holder member 15;

(2) guide sections are provided in sections where the movable internalgear 20 and the stationary internal gear 10 are in contact with eachother; and

(3) the components constituting the different sections of the reductiongear are at least partly formed of a synthetic resin containing areinforcement fiber, or a synthetic resin containing a reinforcementfiber and a lubricant, thereby making it possible to obtain, with a farless number of parts than in the case of conventional small-sizedreduction gears, a small-sized reduction gear which provides a highreduction ratio and a high level of transmission efficiency, whichinvolves little backlash and noise, which excels in dustproofness, andwhich can be produced at low costs. Further, he reduction gear of thepresent invention can be inserted, together with a motor, into acylinder which is to be rotated, thereby making it possible to attain agreat reduction in size as compared to the case where the rotation iseffected with the gears placed outside the cylinder that is to berotated. Thus, it provides a space saving effect. Further, since themotor and the reduction can be lodged together in the cylinder, thevolume of the sound outwardly emitted can be reduced to a very lowlevel, thereby attaining a reduction in noise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view taken along lines X and Y of FIG. 2;

FIG. 2 is a top plane view of a small sized reduction gear constructedin accordance with the invention;

FIG. 3 is a partial sectional exploded view of the invention showing indetail a part of a planetary gear unit;

FIG. 4 is a sectional view of a small-sized reduction gear in accordancewith another embodiment of the present invention;

FIG. 5 is a sectional view of a reduction gear constructed in accordancewith the prior art; and

FIG. 6 is a sectional view of the small sized reduction gear constructedin accordance with the invention as used in a cylinder.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be described withreference to FIGS. 1, 2, 3 and 4. FIG. 2 is a plan view of a small-sizedreduction gear according to the present invention; FIG. 1 is a sectionalview taken along the lines X and Y of FIG. 2; FIG. 3 is a partiallycutaway detailed view of a part of a planetary gear unit; and FIG. 4 isa sectional view showing another embodiment of the small-sized reductiongear of the present invention.

First, the basic structure of the small-sized reduction gear of thepresent invention will be described. In FIG. 1, a small-sized motor 1has a motor boss 2 and a motor shaft 3 which are arranged in alignmentwith the central axis of the small-sized motor 1, and a sun gear 4 isfitted onto the motor shaft 3. Components concentrically arranged withrespect to the motor shaft 3 are: the sun gear 4, a lower case 6, astationary internal gear 10, a holder member 15, a holder clamp 19, amovable internal gear 20, and an upper case 25. Other components areplanet gears 12 and a fastening screw 9. The lower case 6, which isguided and positioned by the motor boss 2, is secured to the small-sizedmotor 1 by the fastening screw 9. The stationary internal gear 10 issecured in position with respect to the lower case 6 by a tooth-shapeddetent 8. The tooth-shaped detent 8 has a tooth-like configuration;when, for example, the lower case 6 is equipped with a male tooth, thestationary internal gear 10 is equipped with a female tooth, the twoteeth being engaged with each other to be fixed in position.

In an exemplary embodiment the number of the planet gears 12 is two. Insome contemplated embodiments as many as four planet gears may beutilized. Planet gears 12 are arranged to be in mesh with and in pointsymmetry with respect to the sun gear 4. The planet gears 12 are also inmesh with the stationary internal gear 10 and the movable internal gear20. The planet gears 12 are held by the holder member 15 and the holderclamp 19 such that their central axes are always kept parallel to thecentral axis of the sun gear 4. These components, arranged in the mannerdescribed above, constitute a planetary gear unit. FIG. 3 shows theplanetary gear unit in detail. Each planet gear 12 has a planet-gearshaft 12a and a planet-gear bearing hole 12b, and is supported at bothends by a shaft and a bearing hole which are respectively provided onthe holder member 15 and the holder clamp 19. The holder member 15includes a planet-gear support stand 15a and planet-gear bearing shafts15b, which serve as a bearing at one end of each planet gear 12, andfurther, columns 15c for positioning and holding the holder clamp 19 inthe vertical direction, guide shafts 15d received by clamp 19 forsecuring the holder clamp 19 in position, and a holder-member bearing15e. The holder clamp 19 includes bearing holes 19a for receiving gearshafts 12a of the planet gears 12, connecting holes 19b for connectingthe holder clamp 19 with the holder member 15, and a holder-clampbearing 19c. By assembling the planet gears 12 by means of the holdermember 15 and the holder clamp 19 and securing them in position, aplanetary gear unit is formed. Although in this embodiment each planetgear 12 is equipped with a shaft and and a bearing hole so as to avoidassembly errors, it is also possible for each planet gear to have shaftsor bearing holes only.

The planetary gear unit is supported at its lower end by theholder-member bearing 15e and a holder-member support section 6a of thelower case 6, and, at its upper end, by the holder-clamp bearing 19c ofthe holder clamp 19 and a holder-clamp support section 20a of themovable internal gear 20. Thus supported at both ends, the planetarygear unit rotates around the sun gear 4. The movable internal gear 20includes an outer peripheral section 20b on the outer side of theinternal teeth section and an output shaft section 20c at the center.The outer peripheral section 20b and the lower case 6 at the lower end,and the output shaft section 20c and the upper case 25 at the upper end,form bearing sections for supporting the unit at both ends movableinternal gears 20 rotates around the central axis of the sun gear 4. Theupper case 25 has a pawl 25a for securing upper case 25, to the lowercase 6, and, while also serving as a bearing for the output shaftsection 20 c, covers the entire small-sized reduction gear. In this way,the movable internal gear 20 is supported by the lower case 6, and theplanetary gear unit is supported at its both ends by the movableinternal gear 20 and the lower case 6, whereby the planetary gear unitcan always be kept parallel to the central axis of the sun gear 4, withthe result that the transmission efficiency of the gears is improved.

The tooth section of each planet gear 12 consists of a planet-gear toothsection A, which is indicated at 12c, and a planet-gear tooth section B,which is indicated at 12d. The planet-gear tooth section A of the planetgear 12, indicated at 12c, is in mesh with both the tooth section of thesun gear 4 and the tooth section of the stationary internal gear 10. Theplanet-gear tooth section B of the planet gear 12, indicated at 12d, isin mesh with the tooth section of the movable internal gear 20.

The planet-gear tooth section A, indicated at 12c, and the planet-geartooth section B, indicated at 12d, of the planet gear 12 have the samenumber (=Z) of teeth. While they are somewhat different in module, thesetooth sections coincide with each other in tooth phase. Accordingly,when the sun gear 4, whose number of teeth is e, starts to rotate, eachplanet gear 12 starts both rotation and revolution since the stationaryinternal gear 10 remains stationary. The number of teeth of thestationary internal gear 10 is n, and the number of teeth of the movableinternal gear 20 is n ±m, m=1 through 4. As a result, the rotation andrevolution of the planet gears 12 causes a difference to be generatedbetween the tooth sections of the stationary internal gear 10 and themovable internal gear 20, whereby the movable internal gear 20 isrotated at a reduced speed. This relationship may be represented asfollows:

    Reduction ratio=(n±m/±m)

In the above expression, m has a valve which ranges from 1 to 4 consistsof an integer, which is the same in both numerator and denominator.

In this way, the rotation of the sun gear 4 transmits to the movableinternal gear 20 a reduced rotation and increased torque, which areoutput to the output shaft section 20c.

As shown in FIG. 2, the number of the planet gears 12 is two.Accordingly, the difference between the number teeth of the movableinternal gear 20 and the number of teeth of the stationary internal gear10 is two. Theoretically, the number of the planet gears might be one.From the viewpoint of balance of forces, however, the number shouldrange from two to four; three is the most preferable number. From theabove formula, however, the number of planet gears is also limited byreduction ratio.

Thus, a high reduction ratio can be achieved through the mesh of a smallnumber of gears, so that the deterioration in transmission efficiencydue to the mesh is small, resulting in a high efficiency of transmissionfrom input to output. As a result, it is possible to generate a largetorque in the output shaft section 20c.

This requires the portion around the output shaft section 20c to bestrong enough to withstand large torque. In this regard, this mechanismhas a structure which is basically capable of withstanding large torque.First, when substituted for the torque of the tooth section of themovable internal gear 20, the output shaft torque is relatively smallbecause of the large distance from the center, so that the force appliedto the tooth section is small. Further, there exist a plurality ofplanet gears 12. Moreover, the mesh ratio between the tooth section ofthe movable internal gear 20 and the tooth sections B of the planetgears 12, indicated at 12d, is large. Due to these factors, the load pertooth applied to the tooth section of the movable internal gear 20, thetooth sections B of the planet gears 12, indicated at 12d, the toothsections A of the planet gears 12, indicated at 12c, and the toothsection of the stationary internal gear 10, may be relatively small. Asa result, an increase in the torque of the output shaft section 20c isattained.

Further, since a high reduction ratio can be attained through acombination of a small number of gears, little backlash is involved.Moreover, since the number of parts is reduced, a small-sized reductiongear is realized which can be produced at low costs. In addition, thereduction gear mechanism is sealed by means of the lower case 6 and theupper case 25, a small-sized reduction gear is realized which involves alow level of noise and which is protected against the intrusion of dust.

As shown in FIG. 3, a first feature of the present invention is that acolumn beam 18 is provided between the columns 15c of the holder member15, thereby substantially increasing the rigidity of the entire holdermember 15. If there were no column beam 18, any load applied to theoutput shaft section 20c would cause a force of action to be applied tothe tooth sections A, 12c, of the planet gears 12, and a force ofreaction to be applied to the tooth sections B, 12d, of the planet gears12, thereby causing a bending force to e applied to the columns 15c ofthe holder 15 to cause a deformation thereof. If the columns 15c arebent, the central axes of the planet gears 12 will be inclined, with theresult that the annulus-row efficiency of the reduction gear mechanismis seriously deteriorated. The column beam 18 will provide a sufficienteffect if it is formed as a straight beam connecting the columns 15cwith each other. In this embodiment, however, the column beam 18 isrounded with arcs which are concentric to the support positions of theplanet gears and which have a diameter larger than the maximum diameterof the planet gears so as to avoid interference with the planet gears12. Due to this arrangement, those sections of the column beam 18 whereit is joined with the columns 15c can be made thick, thereby attaining afurther improvement in rigidity. As a result, the holder 15 is notsubstantially deformed if a bending force is applied thereto, so that itis possible to prevent a deterioration in the annulus-row efficiency ofthis reduction gear mechanism even under a high-load condition.

As shown in FIG. 4, a second embodiment of the present invention is thatthe movable internal gear 20 and the stationary internal gear 10 have,in those sections where they are in contact with each other, holdersections adapted to guide each other. The movable internal gear 20 has,at the lower end of its outer periphery, a ring-likemovable-internal-gear protrusion 21, and the stationary internal gear 10has, at its upper end, a ring-like stationary-internal-gear protrusion11. The inner peripheral surface of the movable-internal-gear protrusion21 and the outer peripheral surface of the stationary-internal-gearprotrusion 11 are fitted together, whereby the movable internal gear 20is guided by the stationary internal gear 10. In the first embodimentdescribed above, in which the positioning of the movable internal gear20 and the stationary internal gear 10 is effected through theintermediation of the lower case 6, the guiding is likely to beperformed inaccurately depending upon the precision of the components.In this embodiment, the movable internal gear 20 and the stationaryinternal gear 10 are directly guided, so that the guiding can beeffected accurately, resulting in an improvement in the transmissionefficiency of the gears. In respect of the tooth strength of thereduction gear, the tooth strength obtained in the above-described firstembodiment is approximately 5 kgf, whereas, in the tooth strengthobtained in this embodiment is approximately 6 kgf, resulting in anincrease in strength of 20%. While the guiding can be effected by themethod described above, it can also be effected by reversing the movableand stationary internal gears, that is, either of them may be on theinner side. Further, the same effect can be obtained by other guidingmethods. For example, it is possible to provide one of the internalgears with a protrusion, and the other one with a recess.

Further, the components of the small-sized reduction gear of the presentinvention may be partly or entirely formed of a synthetic resinreinforced by glass or a reinforcement fiber such as a whisker, or asynthetic resin containing a lubricant such as polyolefine, fluororesinor oil, or a synthetic resin containing both a reinforcement fiber and alubricant, thereby improving the gear transmission efficiency byutilizing the low friction coefficient of a synthetic resin, realizing agear having a high rupture strength through the employment of a highlyrigid material containing a reinforcement resin, and providing alow-noise small reduction gear due to the structure formed of asynthetic resin. Further, by using a liquid crystal polymer having asatisfactory vibration absorbing property, a further reduction in noisecan be achieved.

Examples of the synthetic resin used are as follows: the base polymermay be polyacetal resin, polyamide resin, or polyester resin; the basepolymer may be appropriately blended with carbon fiber, whisker, glassfiber, mica or the like. Such blended synthetic resins are suitable foruse as the material since they provide a satisfactory strength and havea low friction coefficient of 0.2 or less. Those synthetic resins whichconsist of polyacetal resin or polyamide resin blended with anappropriate amount of carbon fiber or whisker are suitable for use asthe material since they have a large flexural strength of 2000 kg/cm² ormore.

Polyamide-type synthetic resins containing a filler or a whisker and alubricant have a high level of strength and a low friction coefficient,so that they are particularly suitable for use as the material. Asynthetic resin whose content of filler or whisker is 20 to 40% andwhose content of the lubricant is 5 to 20% has a flexural strength of2800 kg/cm² and a friction coefficient of approximately 0.1, so thatwhen used as the material for the gear parts and the holder, it helps torealize a small-sized reduction gear which is particularly capable ofwithstanding high torque and which provides a high level of efficiency.Further, the use of a synthetic resin also helps to reduce the weight ofthe small-sized reduction gear.

When used, for example, to move the lens of a still camera, a VCR cameraor the like, or to load or drive a VCR tape, an audio tape or the like,such a small-sized, light-weight and low-noise reduction gear makes itpossible to attain a reduction in the size and weight of the productconcerned. Further, when used in a toy, the small-sized reduction gearalso helps to attain a reduction in size and weight and to realize anefficient utilization of space. For example, it may be used in thedriving section of a toy car or robot for children. In this way, thesmall-sized reduction gear of the present invention has a wide range ofapplications. Further, although the most preferable driving device is amotor, it is also possible to adopt other types of driving devices tothe described small sized reduction gear, such as a spiral spring.

FIG. 6 shows a sectional view of an application example of thesmall-sized reduction gear of the present invention. The small-sizedreduction gear of the present invention is incorporated into a cylinder30. The output shaft section 20c of the small-sized reduction gear isconnected to a connecting section 31 of the cylinder 30, and the torqueof the output shaft section 20c of the small-sized reduction gear istransmitted to the cylinder 30 to rotate the same. Thus, a motor and areduction gear can be incorporated together into a cylinder which is tobe rotated, so that a substantial reduction in size can be attained ascompared to the case where the gear is placed outside the cylinder to berotated, thus obtaining a space saving effect. Further, since the motorand the reduction gear are arranged inside the cylinder, the volume ofthe sound emitted outwardly can be further lowered, thereby attaining areduction in noise. In an example of such an application, theabove-mentioned cylinder 30 is used as a cylinder for winding up the thefilm of a still camera of the type in which the film is extracted fromthe film case and wound around the cylinder 30. By thus applying theinvention to the winding of a film of a still camera, it is possible toutilize the space inside the still camera efficiently, and the qualityof the still camera as a product can be improved through reduction insize, noise and weight. Further, a similar effect can be obtained evenwhen the output shaft section 20c of the reduction gear is, as shown inFIG. 6, not directly connected with the cylinder 30 situated in theperiphery thereof. Further, the output torque of the output shaftsection 20c may be connected to the cylinder 30 in the periphery througha gear, a cam or the like. In that case, the output shaft section 30assumes a configuration corresponding to the gear, cam or the like.

What is claimed is:
 1. A small-sized reduction gear comprising: astationary internal gear (10) having an internal gear whose number ofteeth is n; a movable internal gear (20) moving relative to saidstationary internal gear (10) having an internal gear whose number ofteeth is n±m, where m=1 through 4, and an output shaft (20c), at leastone planet gear (12) each planet gear having z external teeth that meshwith said stationary internal gear (10) and said movable internal gear(20); a holder member (15) and a holder clamp (19), said at least oneplanet gear (12) being supported between said holder member (15) andsaid holder clamp (19); and a sun gear (4) which has e teeth, said sungear meshing with said at least one planet gear (12); a motor shaft 3directly connected to said sun gear (4); at least two columns (15c)extending axially said holder member, and at least one column beam (18)extending radially across said sun gear (4) and mechanically coupled tosaid first columns and said second column.
 2. A small-sized reductiongear comprising: a stationary internal gear (10) having an internal gearwhose number of teeth is n; a movable internal gear (20) moving relativeto stationary internal gear (10) having an internal gear whose number ofteeth is n±m, where m=1 through 4, and an output shaft; at least oneplanet gear (12), each planet gear having z external teeth that meshwith said stationary internal gear (10) and said movable internal gear(20); a holder member (15) and a holder clamp (19), said at least oneplanet gear (12) being supported between said holder member and saidholder clamp; and a sun gear (4) which has e teeth, said sung gearmeshing with said at least one planet gear (12); a motor shaft 3directly connected with said sun gear; and a protrusion (11) formed onand extending coaxially from said stationary internal gear (10) forguiding said movable internal gear (20).
 3. A small-sized reduction gearaccording to claim 1, wherein the components of said reduction gear areat least partly formed of a synthetic resin containing a reinforcementfiber.
 4. A small sized reduction gear according to claim 2, wherein thecomponents of said reduction gear are at least partly formed of asynthetic resin containing a reinforcement fiber.
 5. A small-sizedreduction gear according to claim 1, wherein the components of saidreduction gear are at least partly formed of a synthetic resincontaining a reinforcement fiber and a lubricant.
 6. A small-sizedreduction gear according to claim 2, wherein the components of saidreduction gear are at least partly formed of a synthetic resincontaining a reinforcement fiber and a lubricant.
 7. The small-sizedreduction gear of claim 2, further comprising a second protrusion formedon and extending coaxially from said movable internal gear (20) forguiding said movable internal gear (20).
 8. The small-sized reductiongear of claim 1, further comprising an output shaft formed on saidinternal gear to rotate therewith and a cylinder coupled to said outputshaft to rotate therewith.